Various types of preformed wall sections are known in the art which have two spaced panels and which are interfitted by tongue and groove structure in opposite edges of the panels. Representative panels and tongue groove structure of this type may be found described in one or more of the U.S. Pat. Nos. 1,859,667 Gruner; 2,021,577 Odell; 2,201,175 and 2,231,006 Harshberger; 2,342,682 Miller; 3,315,429 Swanson; 3,817,011 Weed; 3,349,528 Salt; 3,357,146 Gartrell; 3,449,879 Bloom; and 3,305,986 or 3,313,073 Mathews.
In the particular type of preformed wall section wherein two panels are spaced apart by spacing members at least on the opposing edges where the spacing members form the tongue and groove structure, and especially where the tongue and groove is offset in the spacing to lie adjacent one outer panel, there is a problem in interfitting the panels together without damage to the outer panel with an edge extending adjacent the groove. A typical preformed panel may be 96 inches high by 45 inches wide (2.44 M by 1.22 M) with a one inch (2.54 cm) thick tongue extending 1 1/2 inches (3.81 cm). The outer panel may typically be 3/8 inch (0.95 cm) plywood and thus the tongue need tightly fit in interlocked position into the groove along the edge of the panel where the somewhat flexible plywood panel edge 1 1/2 inches wide (3.81 cm) receives a significant portion of the entry force of the groove. Thus, only a very slight angular misalignment between two large panels can exert a force that tends to crack or chip the edge of the panel at the groove or to pull it away from the glue holding it to the separating member. The chipping is even more of a problem when the outer panel adjacent the groove is sheetrock, which is brittle and easily chips. It is readily seen that manual interlocking and fitting of such preformed wall sections can hardly take place without expectation of damage at the interfitting tongue-groove joint.